1. Field of the Invention
The present invention relates to a hydraulic oil storage device, and an injection molding device. Priority is claimed on Japanese Patent Application No. 2012-040000, filed Feb. 27, 2012, the content of which is incorporated herein by reference.
2. Description of Related Art
Conventionally, with regard to large-scale injection molding devices, devices are known that can be separated into injection units and mold clamping units in order to simplify transport and assembly.
In the case of the aforementioned large-scale injection molding device, a storage tank for hydraulic oil and a pump that pumps the hydraulic oil are arranged at the injection unit side for convenience of an installation space. In the large-scale injection molding device, the hydraulic oil that is pumped by this pump is supplied to hydraulic cylinders that are control elements provided at the injection unit and the mold clamping unit. Then, the hydraulic oil that is discharged from each hydraulic cylinder is returned to the storage tank via individual return pipes so that the mutual back pressures do not exert an adverse effect on the hydraulic control.
For that reason, many return pipes that return to the injection unit side the hydraulic oil sent to the mold clamping unit side are arranged between the injection unit and the mold clamping unit. That is to say, with regard to the tube arrangement, a complicated layout resembling a maze is required that must concentrate all the tubing in a narrow space on the injection unit side. For this reason, the design of a large-scale injection molding device has been limited to veteran designers skilled in tubing design. Also, due to the work of connecting the tube joints in a large-scale injection molding device, the assembly work of the large-scale injection molding device has become cumbersome.
Therefore, in order to reduce the number of tubes running between the injection unit and the mold clamping unit, there is known a structure that provides a main tank on the injection unit side, and provides a sub-tank on the mold clamping unit side, and that brings the main tank and the sub-tank into communication with a coupling tube. That is to say, a structure is adopted that couples return pipes that return hydraulic oil from the mold clamping unit to the sub-tank that is provided on the mold clamping unit side, rather than directly connecting them to the main tank that is provided on the injection unit side. By doing so, the hydraulic oil that is pumped to the mold clamping unit can be returned to the main tank via the coupling tube after being once returned to the sub-tank, and so it is possible to reduce the number of tubes that are arranged between the injection unit and the mold clamping unit.
However, with regard to the sub-tank that is provided at the mold clamping unit, only a sub-tank that is smaller than the main tank can be arranged due to the circumstances of the installation space. On the other hand, since the mold clamping unit has a hydraulic cylinder such as a mold clamping cylinder or mold opening/closing cylinder that requires a large flow of hydraulic oil, a large flow of hydraulic oil is returned from the hydraulic cylinder to the sub-tank. Since the movement of hydraulic oil from the sub-tank to the main tank is due mainly to a pressure fluctuation with the main tank accompanying a rise in the sub-tank fluid level, in the case of hydraulic oil flowing in at a high pressure and high flow rate, the movement of the hydraulic oil to the main tank does not keep up with the oil level rise of the sub-tank, and so there has been the possibility of hydraulic oil overflowing from an air breather or the like that is provided at the upper surface of the sub-tank.
Japanese Examined Utility Model Application, Second Publication No. H05-34324 proposes technology that effectively utilizes hydraulic oil that is discharged from a return tube to speed up the flow of the hydraulic oil in the coupling tube, by inserting a flow channel outlet of the return tube with a high hydraulic oil flow rate into the coupling tube that couples the main tank and the sub-tank.
However, in the case of inserting the flow channel outlet of a return tube into the coupling tube in the above manner, in order to sufficiently carry hydraulic oil through the coupling tube, it is necessary to make the return tube diameter (tube opening surface area) approximate the coupling tube diameter. For that reason, due to having a constitution that practically inserts only one return tube into one coupling tube, in the case of a plurality of return tubes being connected to the sub-tank, a plurality of coupling tubes of the same number as the return tubes are required, and so the parts count and assembly time increase. Moreover, as shown in FIG. 5, by forming the distal end side of the return tube 328 bent approximately 90° to the horizontal direction, in the state of the return tube 328 attached to the lid of the sub-tank, it is not possible to insert the return tube 328 in the coupling tube 323 just by attaching the lid of the sub-tank from above. For this reason, when attaching the return tube 328, a worker enters the interior of the sub-tank 322 and, after inserting the distal end of the return tube 328 in the interior of the coupling tube 323, a procedure to fasten the attachment end portion of the return tube 328 to the lid of the sub-tank from the inner side becomes necessary.
Also, when guiding the return tube 328 into the interior of the sub-tank 322 from above the sub-tank 322, in order to insert the flow channel outlet 338 of the return tube 328 into the interior of the coupling tube 323 that extends in a lateral direction, it is necessary to elongate the return tube 328 until the coupling tube 323 that is provided in the vicinity of the bottom surface of the sub-tank 322. Along with that, it is necessary to form the return tube 328 in a bent tube shape within the sub-tank 322. For that reason, due to the discharge reaction force of the hydraulic oil from the flow channel outlet 338, there is a possibility of a bending moment acting on the return tube 328, and excessive vibration being induced by a vortex that occurs at the periphery of the flow channel outlet 338. Also, there is a possibility of the load on fixing members such as the flange 337 of the return tube 328 increasing due to the bending moment and breakage occurring, screws for fastening coming loose from the vibration, and the screws breaking.
Moreover, in the case of leading the return tube 328 to inside the coupling tube 323, due to the drop in pressure that occurs at the space between the outer diameter of the return tube 328 and the inner diameter of the coupling tube 323 due to the Venturi effect of the hydraulic oil that is discharged from the return tube 328, air bubbles are generated in the vicinity of the flow channel outlet 338. In the case of these air bubbles reaching the hydraulic pump, there is a possibility of the hydraulic pump breaking down due to the occurrence of cavitation.
Furthermore, since the return tubes 328 are individually connected to the sub-tank 322 for each control element, due to differences in the flow amount and pressure of the hydraulic oil that flows in, the oil level in the sub-tank 322 undulates and so is not steady. For that reason, pressure fluctuations of the hydraulic oil occur particularly in the vicinity of the coupling tube 323 in the sub-tank 322, and the pressure fluctuations in the vicinity of the coupling tube 323 affect the hydraulic oil of the main tank 321 as pulsations, leading to the possibility of hydraulic control becoming unstable.